1. Standard Operating Procedure for MAPREC test of Type 3 OPV was developed. The in-house MAPREC test for 472-C revertants in Type 3 OPV was performed on all vaccine monopools submitted to FDA for release. The molecular test was performed concurrently with the monkey neurovirulence test and the results were compared.2. Protocols of MAPREC tests for 480- A and 525-C reversions in Type 1, and 481-G reversions in Type 2 OPV were refined, and necessary reagents and control samples prepared and validated. The in-house test of Type 1 and Type 2 OPV lots was initiated by testing a comprehensive set of vaccine monopools made by different manufacturers.3. The WHO International Collaborative Study (ICS) on MAPREC for Type 3 OPV was continued. The results of the first two completed phases of the study were analyzed and reported to the WHO and all the participants. Proposals for the last concluding phase of the study were formulated and submitted to the WHO. The foreign participants of the study were trained by the lab personnel.4. Collaboration with OPV manufacturers aimed at MAPREC introduction for routine in-process vaccine control was initiated. MAPREC test was used to assess acceptability of experimental samples prepared by several institutes. In some cases recommendations on improvement of the virus growth conditions were given.5. Genetic stability of Type 2 OPV was studied by identifying mutations consistently accumulating in African green monkey kidney and Vero cell cultures used for OPV production. Several new mutations were identified, and some preliminary data on their relation to neurovirulence were obtained.The project will be continued. Two papers were published.